Although the subject of considerable study, the function of many chromosomal proteins remains unclear. Obviously, such proteins can perform critical roles in the packaging and regulation of expression of eukaryotic DNA. Among the most interesting of such proteins are the HMG-14 and HMG-17 polypeptides for which evidence has been obtained which indicates a role in maintaining transcribed chromatic regions and the replacement histone variants which accumulate in various adult tissues. The high level of evolutionary conservation of these proteins strongly suggests that they play an important role in eukaryotic development. My lab has isolated genomic and cDNA clones coding for several such proteins of chickens. these clones will be used to prepare a variety of specific mutated chromosomal protein genes. The wild type and mutated genes will then be inserted into Vector DNAs which will allow their expression in cultured cells. These vectors are designed to facilitate transfer of the genes in question into retroviral vectors which can be used to produce infectious avain retroviruses containing the inserted gene. These viral stocks can infect a variety of avian cell lines leading to stable integration of the cloned genes proviral DNA in all infected cells. For most of these experiments, the vectors used will be designed to efficiently express protein corresponding to the inserted chromosomal protein gene, whether mutant or wild type. A variety of phenotypes of the transfected cell lines will be monitored. The level of the transfected chromosomal protein in the cell, in the nucleus nd in chromatic will be compared to the corresponding endogenous proteins. Accumulation and stability of chromosomal proteins and their mRNAs will also be studied. For a limited number of retroviral clones which are of particular interest, the viral stock will be used to infect chick embryos. The viral vectors used in the cases give rise to a non-pathogenic infection of the embryos, so the effect, if any of expressing the mutant (or wild type) chromosomal protein can e studied on the normal growth pattern of the animal. This is particularly important in studying the role of replacement histone variants which only accumulate in the adult animal.